Underwater electrical connection assemblies are known and have been in widespread use in the offshore oil and gas industry for many years. An example is shown in GB 2192316 A, which discloses an underwater connector with a first connector part and a second connector part which are capable of being mated and de-mated underwater. In this known design the first connector half comprises a receptacle for receiving a plug of a second connector half. An electrical contact pin projects axially in the receptacle and when the plug is inserted in the receptacle the pin enters the plug to make an electrical connection with a contact socket inside the plug. The electrical connection is established in a protected oil or gel filled environment contained in a chamber which is pressure balanced with respect to the pressure outside of the connector, thereby reducing the tendency for water or contaminants to enter the connection chamber.
Underwater electrical connectors are used for communicating electric signals for instrumentation and also for electric power applications. In recent years there has been a demand for connector assemblies capable of handling high voltages, typically tens of kilovolts. An example of a high voltage underwater electrical connector is described in GB 2361365 A. The use of high voltages creates issues concerning the electric field around the live components, and the electric stress created in insulating components in the case of high electric field gradients. Insulating materials can suffer from breakdown of the materials above a critical level of electric field gradient. The drawing of high currents through the connector raises issues about heating and it is desirable to avoid hot spots which can lead to reduced efficiency and possible material degradation or even failure.
A known high voltage connector assembly is the SpecTRON (trade mark) produced by Expro Connectors and Measurements of the United Kingdom. The electrical contact pin of the receptacle connector half has an axially extending conductive core and an axially extending annular insulation portion around the axially extending conductive core. The rear end portion of the conductive core has a radially outwardly facing electrical contact surface, for connection to another component to the rear of the connector, such as an underwater cable. The front end portion of the conductive core also has a radially outwardly facing electrical contact surface, in this case for making contact with a socket provided in the plug connector half. The contact pin projects forwardly from a support and when the connector halves are fully mated the base part of the contact pin, nearest the support, extends through a seal provided at the entry to the plug connector half. In the region of this base part the contact pin has an electrically conductive earth shield arranged radially outwardly of the annular insulation portion. This earth shield serves to shield the seal at the entry to the plug connector half from electrical stress. In the mated condition of the connector assembly the base part of the pin immediately adjacent to the support is exposed to the surrounding water, and the earth shield can therefore also serve to protect the annular insulation portion from the effects of ambient water, and thus avoids water absorption that often leads to electrical degradation or failure. It also provides verification testing advantages, because the earth profile is not dependent on the ambient water i.e. it is independent of the environment.
A certain minimum thickness is required for the annular insulation portion between the conductive core and the earth shield, to avoid excessively high electrical stresses in the insulation material. The outside diameter of the earth shield is the same as the outside diameter of the insulation portion forwardly thereof, so that the contact pin has a constant diameter along all of its length which is to be inserted in the entry seal of the plug connector half. In order to comply with these constraints, for a given overall diameter of the contact pin, there is a maximum diameter imposed on the conductive core where it passes through the earth shield.
During construction of this known connector assembly, the annular insulation portion is provided by an insulating sleeve which is inserted over the conductive core from the rear. The rear end portion of the conductive core, where the radially outwardly facing electrical contact surface is provided, therefore has the same diameter as the part of the core which passes through the conductive earth shield.